After bouncing a little yesterday, Facebook (FB -3.7%) is selling off again after Capstone...

After bouncing a little yesterday, Facebook (FB-3.7%) is selling off again after Capstone Investments started coverage with a Hold, citing concerns about its valuation and the performance of its premium ads. It was reported yesterday Facebook, whose ad sales efforts have come under fire, will allow advertisers to buy premium ads via its site, or through third parties. This is likely to boost demand, but could come at the cost of lower ad rates. Zynga (ZNGA-4.4%) is also lower.